Cryptology ePrint Archive: Report 2004/172

Abstract: We construct two efficient Identity Based Encryption (IBE) systems that are selective identity secure {\em without the random oracle model} in groups equipped with a bilinear map. Selective identity secure IBE is a slightly weaker security model than the standard security model for IBE. In this model the adversary must commit ahead of time to the identity that it intends to attack, whereas in the standard model the adversary is allowed to choose this identity adaptively. The first system is based on the decisional bilinear Diffie-Hellman assumption, and extends to give a selective identity Hierarchical IBE secure without random oracles. The second system is based on a related assumption called the bilinear Diffie-Hellman inversion assumption. Applications of either system include an efficient CCA2 public key cryptosystem that supports non-interactive threshold decryption in the standard model, and a simple and practical IBE system that remains secure against full adaptive-ID attacks, under some security penalty, without random oracles.